Workpiece processing method

ABSTRACT

An embodiment of the present disclosure provides a method of processing a workpiece in which a plurality of holes are formed on a surface of the workpiece. The method includes a first sequence including a first process of forming a film with respect to an inner surface of each of the holes and a second process of isotropically etching the film. The first process includes a film forming process using a plasma CVD method, and the film contains silicon.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of U.S. patent application Ser. No.16/111,622, filed on Aug. 24, 2018, which claims priority from JapanesePatent Application No. 2017-162600, filed on Aug. 25, 2017, all of whichare incorporated herein in their entireties by reference.

TECHNICAL FIELD

The present disclosure relates to a method of processing a workpiece.

BACKGROUND

In an electronic device manufacturing process, a mask is formed on aprocessing target layer, and etching is performed to transfer a patternof the mask to the processing target layer. As an example of such anetching, plasma etching may be used. The masks used for plasma etchingare formed by the photolithographic technique. Therefore, a limitdimension of the pattern formed on the processing target layer dependson a resolution of the mask formed by the photolithographic technique.The resolution of the pattern of the mask has a resolution limit. Thereis a growing demand for high integration of an electronic device and itis required to form a pattern having a dimension smaller than theresolution limit. For this reason, as disclosed in, for example, U.S.Patent Application Publication No. 2016/0379824, a technique has beenproposed in which the dimensional shape of the pattern is adjusted toreduce the width of an opening of the pattern.

SUMMARY

In an aspect of the present disclosure, a method of processing aworkpiece is provided. A plurality of holes are provided on the surfaceof the workpiece. This method has a first sequence that includes a firstprocess of forming a film on the inner surface of a hole and a secondprocess of isotropically etching the film. The first process includes afilm forming process using a plasma CVD method, and the film containssilicon.

The foregoing summary is illustrative only and is not intended to be inany way limiting. In addition to the illustrative aspects, exemplaryembodiments, and features described above, further aspects, exemplaryembodiments, and features will become apparent by reference to theaccompanying drawings and the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart illustrating a portion of a method according toan embodiment.

FIG. 2 is a cross-sectional view illustrating a workpiece to which themethod illustrated in FIG. 1 is applied.

FIG. 3 illustrates an example of a plasma processing apparatus that maybe used to execute the method illustrated in FIG. 1.

FIG. 4 is a cross-sectional view illustrating the state of a workpieceafter a film is formed in the step illustrated in FIG. 1.

FIG. 5 is a view schematically illustrating the change in a hole widthwhen the sequence illustrated in FIG. 1 is repeatedly executed.

FIG. 6 is a view illustrating a relationship between the isotropy ofetching and a pressure in the step illustrated in FIG. 1.

FIG. 7 is a flow chart illustrating another example of an etching stepincluded in the method illustrated in FIG. 1.

FIG. 8 is a cross-sectional view illustrating the state of the workpieceafter surface modification in the method illustrated in FIG. 7.

FIG. 9 illustrates the self-controllability of surface modification inthe sequence illustrated in FIG. 7.

FIGS. 10A to 10C are views illustrating the principle of etching in thestep illustrated in FIG. 7.

FIG. 11 is a view illustrating the changes in the amount of etching andthe thickness of a mixed layer formed on the film during the executionof the sequence illustrated in FIG. 7.

FIG. 12 is a cross-sectional view illustrating the state of theworkpiece after a two-layered film is formed in the film forming stepillustrated in FIG. 1.

FIG. 13 is a flow chart illustrating an example of forming thetwo-layered film in the film forming step illustrated in FIG. 1.

FIG. 14 is a view illustrating a correlation between the amount ofoxygen added during film formation and the etching resistance of thefilm.

FIG. 15 is a view schematically illustrating the change in the holewidth that may occur when the film forming step illustrated in FIG. 1forms the two-layered film and the sequence illustrated in FIG. 1 isrepeatedly executed.

FIG. 16 is a flow chart illustrating another example of the film formingstep illustrated in FIG. 13.

FIGS. 17A to 17C are views illustrating the principle of the filmformation in the step illustrated in FIG. 16.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part thereof. The illustrativeexemplary embodiments described in the detailed description, drawings,and claims are not meant to be limiting. Other exemplary embodiments maybe utilized, and other changes may be made without departing from thespirit or scope of the subject matter presented here.

Pattern formation may be achieved by forming a highly detailed hole withrespect to a processing target layer such as, for example, a SiO₂ layer.When forming a pattern that has a dimension smaller than the resolutionlimit of the mask pattern, it is required to control a very detailedminimum line width (CD: critical dimension) of the pattern hole. As thepattern becomes more detailed, the influence of the minimum line widthvariation becomes greater. In particular, in the case of an extremeultra violet (EUV) lithography, the initial local CD uniformity (LCDU)may decrease. Therefore, in the pattern formation on a workpiece havinga processing target layer such as, for example, SiO₂, it is desired toimplement a method of suppressing the minimum line width variation to ahigh precision in order to achieve minimization due to high integration.

In an aspect of the present disclosure, a method of processing aworkpiece is provided. A plurality of holes are provided on the surfaceof the workpiece. This method has a first sequence that includes a firstprocess of forming a film on the inner surface of a hole and a secondprocess of isotropically etching the film. The first process includes afilm forming process using a plasma CVD method, and the film containssilicon.

In the above-described method, since the first process includes a filmforming process that uses a plasma-enhanced chemical vapor deposition(CVD) method, a film having a relatively thin film thickness is formedwith respect to a hole having a relatively narrow hole width and a filmhaving a relatively thick film thickness is formed with respect to ahole having a relatively wide hole width. Therefore, even when the holewidth varies in a plurality of holes, the variation may be reduced bythe film forming process in the first process. Further, in the secondprocess, since the film formed by the first process is isotropicallyetched, the film formed by the first process maintains a state in whichthe hole width variation is reduced, while adjusting the hole width.

According to an embodiment, a first sequence is repeatedly executed.

Since the first sequence is repeatedly executed in this manner, a filmhaving the desired film thickness may be finally formed by forming afilm having a relatively thin film thickness in the first process andrepeatedly executing the first sequence. Thus, it is possible tosufficiently avoid the situation where the opening of a hole having arelatively narrow hole width is occluded by the film formed by the firstprocess.

According to the embodiment, in the second process, the film isisotropically etched by removing the film for each atomic layer byexecuting a second sequence that includes: a third process of generatingplasma of a first gas within a processing container of a plasmaprocessing apparatus in which a workpiece is accommodated, andisotropically forming a mixed layer that includes an ion included in theplasma of the first gas in the atomic layer of the inner surface of thehole; a fourth process of purging a space within the processingcontainer after executing the third process; a fifth process ofgenerating plasma of a second gas within the processing container andremoving the mixed layer by radicals included in the plasma of thesecond gas after executing the fourth process; and a sixth process ofpurging the space within the processing container after executing thefifth process. The first gas includes nitrogen, the second gas includesfluorine, and the plasma of the second gas generated in the fifthprocess includes the radial that removes the mixed layer including asilicon nitride. In this manner, after the surface of the film formed bythe first process is isotropically modified by a method which is thesame as the atomic layer etching (ALE) method, and the mixed layer isisotropically formed on the surface of the film, the mixed layer isentirely removed. Thus, the film formed in the first process may beisotropically and uniformly removed by the etching performed in thesecond process.

According to the embodiment, the second gas may be a mixed gas thatincludes NF₃ gas or O₂ gas, a mixed gas that includes NF₃ gas, O₂ gas,H₂ gas, and Ar gas, or a mixed gas that includes CH₃F gas, O₂ gas, andAr gas. Thus, a second gas containing fluorine may be implemented.

According to the embodiment, the film includes a first film and a secondfilm, and the first process includes: a seventh process of forming thefirst film on the inner surface of the hole; and an eighth process offorming the second film on the first film. An etching resistance foretching performed in the second process is lower in the first film sidethan the second film side.

Even when the second film is removed in the second process from the holewhere the film having a relatively thin film thickness is formed in thefirst process due to a relatively narrow hole width (referred to as afirst hole), at this time point, a portion of the second film may remainin the hole where the film having a relatively thick film thickness isformed in the first process due to a relatively wide hole width(referred to as a second hole). When the etching in the second processis continuously performed from this state, since the etching resistanceof the first film is lower than the etching resistance of the secondfilm, the etching proceeds more quickly in the first hole side than thesecond hole side. Therefore, it is possible to more effectively reducethe variation in the hole width between the first hole and the secondhole using the first film having a relatively low etching resistance andthe second film having a relatively high etching resistance.

According to the embodiment, in the seventh process, the first film isformed by repeatedly executing a third sequence that includes: a ninthprocess of supplying a third gas to a processing container of a plasmaprocessing apparatus in which the workpiece is accommodated; a tenthprocess of purging a space within the processing container afterexecuting the ninth process; an eleventh process of generating plasma ofa fourth gas within the processing container after executing the tenthprocess; and a twelfth process of purging the space within theprocessing container after executing the eleventh process. The secondfilm is formed using a plasma CVD in the eighth process, the third gasincludes an aminosilane-based gas, the fourth gas includes a gascontaining an oxygen atom, and plasma of the third gas is not generatedin the ninth process. Thus, since the first film is formed by the samemethod as the atomic layer deposition (ALD) method, the first filmhaving a relatively thin film thickness may be formed in a conformalmanner in the seventh process. Therefore, even when the second film isformed by the plasma CVD method, the entire thickness of the filmincluding the first film and the second film may be effectivelycontrolled.

According to the embodiment, the third gas includes monoaminosilane.Thus, the reaction precursor of silicon may be formed using a third gasincluding monoaminosilane.

According to the embodiment, the aminosilane-based gas of the third gasmay include aminosilance having one to three silicon atoms. Theaminosilane-based gas of the third gas may include aminosilane havingone to three amino groups. In this manner, the aminosilane-based gas ofthe third gas may use aminosilane having one to three silicon atoms.Further, aminosilane having one to three amino groups may be used as theaminosilane-based gas of the third gas.

In another aspect of the present disclosure, a method of processing aworkpiece is provided. A plurality of holes are provided on the surfaceof the workpiece. The method includes a first sequence that includes: afirst process of forming a film with respect to an inner surface of eachof the holes using a plasma CVD; and a second process of isotropicallyetching the film. The film includes a first film and a second film onthe first film, and an etching resistance for etching performed in thesecond process is lower in a first film than a second film.

According to another embodiment, each of the first and second films maybe any one of a silicon-containing film, a boron-containing film, ametal film, and a carbon-containing film.

As described above, there is provided a method of suppressing theminimum line width variation to a high precision in the patternformation on a workpiece.

Hereinafter, various embodiments will be described in detail withreference to the accompanying drawings. The same or equivalent portionsare denoted by the same reference numerals in each drawing. FIG. 1 is aflow chart illustrating a portion of the method according to theembodiment (hereinafter, referred to as a “method MT”). The method MTillustrated in FIG. 1 is an embodiment of a method of processing aworkpiece (hereinafter, referred to as a “wafer W”). FIG. 2 is across-sectional view illustrating the wafer W to which the method MTillustrated in FIG. 1 is applied.

The wafer W illustrated in FIG. 2 includes a processing target layer EL,a mask MK formed on the processing target layer EL (the surface EL1 ofthe processing target layer EL), and a hole formed in the mask MK. (Thehole is, e.g., a hole HL1 and a hole HL2. In the present embodiment,other similar shapes such as a hole, a pit, a depression, and a recessmay be included.) In the wafer W, a plurality of holes are formed on thesurface of the wafer W. In the present embodiment, the hole is formed inthe mask MK, but the present disclosure is not limited to aconfiguration in which the holes are formed in the mask MK.

The processing target layer EL is, for example, a Si antireflectionfilm, that is, an anti-reflection coating (SiARC) film. The material ofthe mask MK includes a resist according to the embodiment. In the maskMK, a hole of a pattern that provides an opening (which is equivalent toa hole formed on the surface of the wafer W) is formed byphotolithography. The hole of the mask MK is formed substantially overthe entire surface of the wafer W. The holes HL1 and HL2 of the wafer Willustrated in FIG. 2 have different hole widths. The hole HL1 has ahole width WW1 a and the hole HL2 has a hole width WW1 b. In the holesHL1 and HL2 illustrated in FIG. 2, the value of the hole width WW1 a issmaller than the value of the hole width WW1 b.

The method MT (method of processing the workpiece) is executed by aplasma processing apparatus 10. FIG. 3 illustrates an example of theplasma processing apparatus that may be used to execute the methodillustrated in FIG. 1. FIG. 3 schematically illustrates across-sectional structure of the plasma processing apparatus 10 that maybe used in various embodiments of the method MT of processing the waferW. The plasma processing apparatus 10 illustrated in FIG. 3 includes aninductively coupled plasma (ICP) type plasma source. The plasmaprocessing apparatus 10 includes a processing container 192 that isformed in a cylindrical shape (e.g., a cylindrical shape according tothe embodiment) made of metal (e.g., aluminum according to theembodiment). The processing container 192 defines a processing space Spin which the plasma processing is performed. The shape of the processingcontainer 192 is not limited to a cylindrical shape, and may be arectangular shape such as a box shape according to the embodiment. Theplasma source of the plasma processing apparatus 10 is not limited to anICP type, and may be, for example, an electron cyclotron resonance (ECR)type, a capacitively coupled plasma (CCP) type, or a microwave type.

A pedestal PD which places the wafer W is provided in a bottom portionof the processing container 192. The pedestal D includes anelectrostatic chuck ESC and a lower electrode LE. The lower electrode LEincludes a first plate 18 a and a second plate 18 b. The processingcontainer defines the processing space Sp.

A support 14 is provided in the bottom portion of the processingcontainer 192 inside the processing container 192. According theembodiment, the support 14 has, for example, a substantially cylindricalshape. The support 14 is made of, for example, an insulating materialaccording the embodiment. The insulating material constituting thesupport 14 may include oxygen such as quartz. The support 14 extendsfrom the bottom portion of the processing container 192 in the verticaldirection in the processing container 192 (the direction toward thesurface of the wafer W placed on the electrostatic chuck ESC from theceiling side of the processing container 192 (specifically, e.g., on aplate-like dielectric side 194)).

The pedestal PD is placed in the processing container 192. The pedestalPD is supported by the support 14. The pedestal PD holds the wafer W onthe top surface of the pedestal PD. The wafer W is a workpiece. Thepedestal PD includes a lower electrode LE and an electrostatic chuckESC.

The lower electrode LE includes a first plate 18 a and a second plate 18b. The first plate 18 a and the second plate 18 b are made of metal, forexample, aluminum according to the embodiment. The first plate 18 a andthe second plate 18 b have, for example, a substantially disk shapeaccording to the embodiment. The second plate 18 b is provided on thefirst plate 18 a. The second plate 18 b is electrically connected to thefirst plate 18 a.

The electrostatic chuck ESC is provided on the second plate 18 b. Theelectrostatic chuck ESC has a structure in which electrodes of aconductive film are disposed between a pair of insulating layers orbetween a pair of insulating sheets. A direct current power supply 22 iselectrically connected to the electrode of the electrostatic chuck ESCvia a switch 23. The electrostatic chuck ESC sucks the wafer W by theelectrostatic force generated by the direct current voltage from thedirect current power supply 22. As a result, the electrostatic chuck ESCmay hold the wafer W.

A focus ring FR is arranged on the periphery of the second plate 18 b soas to surround the edge of the wafer W and the electrostatic chuck ESC.The focus ring FR is provided to improve the uniformity of the etching.The focus ring FR is made of materials appropriately selected dependingon the material of the film to be etched, and may be made of, forexample, quartz according to the embodiment.

A coolant flow path 24 is provided inside the second plate 18 b. Thecoolant flow path 24 constitutes a temperature control mechanism. Acoolant is supplied to the coolant flow path 24 from a chiller unitprovided outside the processing container 12 via a pipe 26 a. Thecoolant supplied to the coolant flow path 24 is returned to the chillerunit via the pipe 26 b. In this manner, the coolant is supplied to thecoolant flow path 24 so that the coolant circulates. By controlling thetemperature of the coolant, the temperature of the wafer W supported bythe electrostatic chuck ESC is controlled. According to the embodiment,a gas supply line 28 supplies a heat transfer gas, for example, He gasfrom a heat transfer gas supply mechanism between the top surface of theelectrostatic chuck ESC and the back surface of the wafer W.

The plasma processing apparatus 10 is provided with a temperaturecontroller HT that adjusts the temperature of the wafer W. Thetemperature controller HT is built in the electrostatic chuck ESC. Aheater power supply HP is connected to the temperature controller HT. Bysupplying power to the temperature controller HT from the heater powersupply HP, the temperature of the electrostatic chuck ESC is adjustedand the temperature of the wafer W displaced on the electrostatic chuckESC is adjusted. The temperature controller HT may be embedded in thesecond plate 18 b.

The temperature controller HT includes a plurality of heating elementsthat generate heat and a plurality of temperature sensors that detecttemperatures of the respective surroundings of the plurality of heatingelements.

The plate-like dielectric 194 is disposed above the pedestal PD to facethe pedestal PD. The lower electrode LE and the plate-like dielectric194 are provided substantially in parallel with each other. A processingspace Sp is provided between the plate-like dielectric 194 and the lowerelectrode LE. The processing space Sp is a spatial region that performsa plasma processing on the wafer W.

In the plasma processing apparatus 10, a deposit shield 46 is providedso as to be detachable along the inner wall of the processing container12. The deposit shield 46 is also provided on the outer periphery of thesupport 14. The deposit shield 46 suppresses an etching by-product(deposit) from being attached to the processing container 12 and may beconstituted by coating an aluminum material with ceramics such as Y₂O₃.In addition to Y₂O₃, the deposit shield may be made of a materialincluding, for example, quartz, according to the embodiment.

An exhaust plate 48 is provided on the bottom portion of the processingcontainer 192 and between the support 14 and the side wall of theprocessing container 192. The exhaust plate 48 may be constituted, forexample, by coating an aluminum material with ceramics such as Y₂O₃. Anexhaust port 12 e is provided below the exhaust plate 48 in theprocessing container 12. An exhaust device 50 is connected to theexhaust port 12 e via an exhaust pipe 52. The exhaust device 50 has avacuum pump such as a turbo molecular pump so that the space in theprocessing container 12 may be reduced to a desired degree of vacuum. Ahigh-frequency power source 64 is a power source that generates ahigh-frequency power for drawing ions into the wafer W, that is, ahigh-frequency bias power, and generates a high-frequency bias powerhaving a frequency within the range of 400 kHz to 40.68 MHz, forexample, 13 MHz. The high-frequency power source 64 is connected to thelower electrode LE via a matching device 68. The matching device 68 is acircuit that matches an output impedance of the high-frequency powersource 64 with an input impedance of a load side (lower electrode LEside).

In a ceiling portion of the processing container 192, the plate-likedielectric 194 made of, for example, quartz glass or ceramics isprovided so as to face the pedestal PD according to the embodiment.Specifically, according to the embodiment, the plate-like dielectric 194is formed, for example, in a disk shape and is hermetically attached soas to close an opening formed in the ceiling portion of the processingcontainer 192. The processing space Sp is a space in which plasma isgenerated by a plasma source. The processing space Sp is a space inwhich the wafer W is placed.

The processing container 192 is provided with a gas supply unit 120 thatsupplies a plurality of types of processing gases (e.g., processinggases G1 to G8 described below according to the embodiment). The gassupply unit 120 supplies various processing gases to the processingspace Sp described above. A gas introduction port 121 is formed in theside wall of the processing container 192, and a gas supply source 122is connected to the gas introduction port 121 via a gas supply pipe 123.A flow controller (e.g., a mass flow controller 124 and an open/closevalve 126) is provided in the middle of the gas supply pipe 123 tocontrol the flow rate of various processing gases. With such a gassupply unit 120, various processing gases output from the gas supplysource 122 are controlled at the flow rate set in advance by the massflow controller 124, and are supplied from the gas introduction port 121to the processing space Sp of the processing container 192.

In FIG. 3, for simplicity of description, the gas supply unit 120 isrepresented by a single gas line, but the gas supply unit 120 isconfigured to supply a plurality of gas species. The gas supply unit 120illustrated in FIG. 3 is configured to supply gas, for example, from theside wall of the processing container 192. However, the gas supply unit120 is not limited to the configuration illustrated in FIG. 3. Forexample, the gas supply unit 120 may be configured to supply gas fromthe ceiling portion of the processing container 192. When the gas supplyunit 120 has such a configuration, for example, a gas introduction portmay be formed at the central portion of the plate-like dielectric 194,and the gas may be supplied from the gas introduction port.

An exhaust device 50 that exhausts the atmosphere in the processingcontainer 192 is connected to the bottom portion of the processingcontainer 192 via an exhaust pipe 52. The exhaust device 50 isconstituted by, for example, a vacuum pump, and the pressure in theprocessing container 192 may be set to a preset pressure.

A wafer carry-in/carry-out port 134 is formed on the side wall of theprocessing container 192, and a gate valve 136 is provided on the wafercarry-in/carry-out port 134. For example, when the wafer W is carriedin, the gate valve 136 is opened. After the wafer W is placed on thepedestal PD in the processing container 192 by a transfer mechanism suchas a transfer arm (not illustrated), the gate valve 136 is closed andthe processing of the wafer W is started.

A planar high-frequency antenna 140 and a shield member 160 that coversthe high-frequency antenna 140 are provided on the top side surface(outer side surface) of the plate-like dielectric 194 on the ceilingportion of the processing container 192. The high-frequency antenna 140according to the embodiment includes an inner antenna element 142Adisposed in the central portion of the plate-like dielectric 194 and anouter antenna element 142B disposed to surround the outer periphery ofthe inner antenna element 142A. Each of the inner antenna element 142Aand the outer antenna element 142B is a conductor such as copper,aluminum, or stainless steel according to the embodiment, and has aspiral coil shape.

The inner antenna element 142A and the outer antenna element 142B areboth sandwiched by a plurality of pinching members 144 and areintegrated with each other. The pinching member 144 has, for example, arod shape according to the embodiment. The pinching member 144 isdisposed radially so as to protrude from the center of the inner antennaelement 142A to the outside of the outer antenna element 142B.

The shield member 160 includes an inner shield wall 162A and an outershield wall 162B. The inner shield wall 162A is provided between theinner and outer antenna elements 142A and 142B so as to surround theinner antenna element 142A. The outer shield wall 162B is provided so asto surround the outer antenna element 142B, and has a cylindrical shape.Therefore, the top side surface of the plate-like dielectric 194 isdivided into a central portion on the inside of the inner shield wall162A (central zone) and a peripheral portion between the inner shieldwall 162A and the outer shield wall 162B (peripheral zone).

A disk-shaped inner shield plate 164A is provided on the inner antennaelement 142A to block the opening of the inner shield wall 162A. Anouter shield plate 164B having a donut plate shape is provided on theouter antenna element 142B so as to block the opening between the innershield wall 162A and the outer shield wall 162B.

The shape of the shield member 160 is not limited to a cylindricalshape. The shape of the shield member 160 may be, for example, arectangular shape or the like according to the embodiment, or may bematched to the shape of the processing container 192. Here, since theprocessing container 192 has, for example, a substantially cylindricalshape according to the embodiment, the shield member 160 also has asubstantially cylindrical shape corresponding to the cylindrical shape.When the processing container 192 has a substantially rectangular shape,the shield member 160 also has a substantially rectangular shape.

A high-frequency power source 150A and a high-frequency power source150B are connected to the inner antenna element 142A and the outerantenna element 142B, respectively. Thus, a high frequency having thesame frequency or different frequency may be applied to each of theinner and outer antenna elements 142A and 142B. For example, when a highfrequency power having a frequency, for example, 27 MHz is supplied fromthe high-frequency power source 150A to the inner antenna element 142Aat a preset power W according to the embodiment, the gas introduced intothe processing container 192 is excited by the induction magnetic fieldformed in the processing container 192, and donut shape plasma may begenerated in the central portion of the wafer W. In addition, when ahigh frequency power having a frequency, for example, 27 MHz is suppliedfrom the high-frequency power source 150B to the outer antenna element142B at a preset power W according to the embodiment, the gas introducedinto the processing container 192 is excited by the induction magneticfield formed in the processing container 192, and donut shape plasma maybe generated in the peripheral portion of the wafer W. The highfrequencies output from each of the high-frequency power source 150A andthe high-frequency power source 150B are not limited to theabove-described frequencies, but various frequencies may be suppliedfrom each of the high-frequency power source 150A and the high-frequencypower source 150B. It is necessary to adjust the electrical lengths ofthe inner and outer antenna elements 142A and 142B in accordance withthe high frequency output from each of the high-frequency power source150A and the high-frequency power source 150B. In each of the innershield plate 164A and the outer shield plate 164B, the height may beadjusted separately by an actuator 168A and an actuator 168B.

A controller Cnt is a computer that includes a processor, a storageunit, an input device, a display device, and the like, and controls therespective portions of the plasma processing apparatus 10 which will bedescribed later. The controller Cnt is connected to a mass flowcontroller 124, an open/close valve 126, a high-frequency power source150A, a high-frequency power source 150B, a direct current power supply22, a switch 23, an exhaust device 50, a high-frequency power source 64,a matching device 68, an electrostatic chuck ESC, a heater power supplyHP, a chiller unit, or the like. The controller Cnt operates inaccordance with a computer program that controls the respective portionsof the plasma processing apparatus 10 in the respective steps of themethod MT (a program based on the input recipe), and sends out a controlsignal. The respective portions of the plasma processing apparatus 10are controlled by a control signal from the controller Cnt. Thecontroller Cnt may control the selection and flow rate of the gassupplied from the gas supply source 122, the exhaust of the exhaustdevice 50, the power supply from the high-frequency power sources 150Aand 150B, the power supply from the high-frequency power source 64, thepower supply from the heater power supply HP, the flow rate andtemperature of the coolant from the chiller unit, or the like, forexample, by the control signal from the controller Cnt. The respectivesteps of the method MT disclosed in the present specification may beexecuted by operating each portion of the plasma processing apparatus 10by control by the controller Cnt. A computer program that executes themethod MT and various data used to execute the method MT are stored inthe storage unit of the controller Cnt in a readable manner.

Referring back to FIG. 1, the method MT will be described in detail,taking an example of a form implemented in a processing system 1provided with the plasma processing apparatus 10. The method MT is aprocessing method of adjusting the variation of the hole width (a methodof processing the workpiece). The method MT may also be executed onanother plasma processing apparatus different from the plasma processingapparatus 10. The method MT includes a sequence SQ1 and a step ST3 asillustrated in FIG. 1. The sequence SQ1 includes a step ST1 (first step)and a step ST2 (second step). First, the wafer W is carried into theprocessing container 192 of the plasma processing apparatus 10 beforethe execution of the step ST1, and the wafer W carried into theprocessing container 192 of the plasma processing apparatus 10 ispositioned and placed onto the electrostatic chuck ESC.

In the step ST1, a film is formed on the inner surface of the hole onthe surface of the wafer W. The step ST1 includes a film forming processthat uses a plasma-enhanced chemical vapor deposition (CVD) method.According to the embodiment, for example, the step ST1 includes a filmforming process of generating plasma of the processing gas G1 within theprocessing container 192 of the plasma processing apparatus 192 in whichthe wafer W is accommodated, and forming a film LA with respect to thesurface of the wafer W (the inner surface (side surface and bottomsurface) of a surface MK1 and a hole (including holes HL1 and HL2) of amask MK) by the plasma CD method. The film LA formed by the step ST1contains a silicon oxide and may contain, for example, SiO₂ according tothe embodiment.

In the step ST1, the processing gas G1 is supplied to the processingcontainer 192 to generate plasma of the processing gas G1 at a statewhere the wafer W is placed on the electrostatic chuck ESC. Theprocessing gas G1 contains a gas species having a superior depositionproperty and contains, for example, silicon according to the embodiment.According to the embodiment, the processing gas G1 may be a mixed gas ofSiCl₄ and He (according to the embodiment, the gas flow rates are 25sccm (SiCl₄) and 100 sccm (He), respectively), a mixed gas of SiCl₄,CH₄, H₂, Ar (according to the embodiment, the gas flow rates are 20 sccm(SiCl₄), 100 sccm (CH₄), 100 sccm (H₂), and 800 sccm (Ar),respectively), or the like. The processing gas G1 is supplied from theselected gas source of a plurality of gas sources of the gas supplysource 122 into the processing container 192. A high frequency power(e.g., 60 MHz and 300 to 1000 W according to the embodiment) is suppliedfrom the high-frequency power source 150A and the high-frequency powersource 150B, and the exhaust device 50 is operated to set the pressureof the processing space Sp in the processing container 192 to a presetvalue (e.g., 50 mTorr according to the embodiment). The execution timeof the step ST1 is, for example, 60 s according to the embodiment. Sincethe processing gas G1 contains a gas species having a superiordeposition property, the film thickness of the film LA formed in thestep ST1 is relatively thin with respect to the inner surface having arelatively small hole HL1 and is relatively thick with respect to theinner surface having a relatively wide hole width, as illustrated inFIG. 4. FIG. 4 is a cross-sectional view illustrating the state of thewafer W after the film is formed in the step illustrated in FIG. 1. Thevalue of a film thickness WF1 a of the film LA formed on the innersurface of the hole HL1 is smaller than a film thickness WF1 b of thefilm LA formed on the inner surface of the hole HL2.

In the step ST2 following the step ST1, the film thickness of the filmLA is adjusted. More specifically, the film LA is isotropically etchedin the step ST2. In the step ST2, the film LA is isotropically etched toadjust the film thickness of the film LA. In the step ST2, theprocessing gas G2 is supplied to the processing container 192 togenerate plasma of the processing gas G2 at a state where the wafer W isplaced on the electrostatic chuck ESC. The processing gas G2 includesfluorine and may be, for example, Cl₂ gas (according to the embodiment,the flow rate of the gas is 200 sccm), a mixed gas of C₄F₈ and Ar(according to the embodiment, the gas flow rates are 40 sccm (C₄F₈) and200 sccm (Ar), respectively), or the like according to the embodiment.The processing gas G2 is supplied from the selected gas source of aplurality of gas sources of the gas supply source 122 into theprocessing container 192. A high frequency power (e.g., 60 MHz and 500 Waccording to the embodiment) is supplied from the high-frequency powersource 150A and the high-frequency power source 150B, and the exhaustdevice 50 is operated to set the pressure of the processing space Sp inthe processing container 192 to a preset value (e.g., 400 mTorraccording to the embodiment). The execution time of the step ST2 is, forexample, 30 s according to the embodiment.

When the film thickness of the film LA formed in the step ST1 isrelatively thick with respect to the hole HL1 having a relatively smallhole width, the opening of the hole HL1 may be occluded by the film LA.In order to avoid such a case, the film LA formed in the step ST1 isformed to be sufficiently thin so that the opening of the hole HL1 isnot occluded, and the sequence SQ1 including the steps ST1 and ST2(first sequence) is repeated until the film thickness of the film LAreaches a desired value. In this manner, by repeating the sequence SQ1while sufficiently reducing the film thickness of the film LA formed inthe step ST1, the film LA having the desired film thickness may beformed on the inner surface of the hole without occluding the opening ofthe hole.

The change in the hole width in the sequence SQ1 will be described withreference to FIG. 5. FIG. 5 is a view schematically illustrating thechange in a hole width that occur when the sequence illustrated in FIG.1 is repeatedly executed. A line G1 a represents the change in the holewidth of the hole HL1, and a line G2 a represents the change in the holewidth of the hole HL2. When the film LA is formed in the step ST1, thefilm LA is relatively thin in the hole HL1 having a relatively narrowhole width, and the film LA is relatively thick in the hole HL2 having arelatively wide hole width. Thus, the difference between the hole widthin the hole HL2 and the hole width in the hole HL1 (difference H2 a) atthe end of the step ST1 is smaller than the difference at the start ofthe step ST1 (difference H1 a). Since isotropic etching is performed inthe step ST2 following the step ST1, the film LA is etched while thedifference in the hole width between the hole HL2 and the hole HL1(difference H2 a) is maintained constantly. Therefore, the difference inthe hole width between the hole HL2 and the hole HL1 at the end of thestep ST2 (difference H2 a) is maintained as in the case of the start ofthe step ST2. In this manner, every time the sequence SQ1 is executed,the difference in the hole width between the hole HL2 and the hole HL1is reduced stepwise, and by executing the sequence SQ1 a plurality oftimes, the difference converges within a desired range so that thevariation of the holes of the wafer W may be sufficiently reduced.

Subsequently, the conditions for causing the etching of the step ST2 tohave isotropy will be described. FIG. 6 is a view illustrating arelationship between the isotropy of etching and a pressure in the stepST2 illustrated in FIG. 1. The vertical axis in FIG. 6 represents anetching amount (nm), and the horizontal axis in FIG. 6 represents thepressure (mTorr) in the processing space Sp. A line GRa in FIG. 6represents the change in the etching amount of the bottom side of thehole (vertical side), a line GRb in FIG. 6 represents the change in theetching amount of the lateral side of the hole (horizontal side), and aline GRc in FIG. 6 represents the change in the value obtained bydividing the etching amount of the bottom side of the hole (verticalside) by the etching amount of the lateral side of the hole (horizontalside) (horizontal ratio). As illustrated in FIG. 6, when the pressure ofthe processing space Sp is relatively high (200 mTorr) or more (e.g.,approximately 400 mTorr according to the embodiment), sufficientlyisotropic etching may be implemented in the step ST2.

<Modification of Step ST2>

The isotropic etching of the step ST2 may be implemented by the methodillustrated in, for example, FIG. 7 according to the embodiment. Themethod illustrated in FIG. 7 is a method of etching the film LAisotropically and uniformly by the same method as the atomic layeretching (ALE) method, regardless of the hole width and the hole density.In the meantime, the isotropic etching of the step ST2 is not limited tothe method illustrated in FIG. 7. FIG. 7 is a flow chart illustratinganother example of the step ST2 included in the method illustrated inFIG. 1. The step ST2 illustrated in FIG. 7 includes a sequence SQ2(second sequence) and a step ST2 e. The sequence SQ2 includes the stepST2 e (third step), a step ST2 b (fourth step), a step ST2 c (fifthstep), and a step ST2 d (sixth step).

In the step ST2 a, plasma of the processing gas G3 (first gas) isgenerated in the processing container 192 of the plasma processingapparatus 10 in which the wafer W is accommodated, and a mixed layer MXthat includes the ions included in the plasma of the processing gas G3is isotropically and uniformly formed with respect to the atomic layeron the inner surface of the hole. In the step ST2 a, the mixed layer MXthat includes the ions included in the plasma of the processing gas G3may be isotropically and uniformly formed with respect to the atomiclayer on the surface of the film LA. In the step ST2 a, the processinggas G3 is supplied to the processing container 192 to generate plasma ofthe processing gas G3 at a state where the wafer W is placed on theelectrostatic chuck ESC. The processing gas G3 includes nitrogen, andaccording to the embodiment, may include, for example, N₂ gas (the gasflow rate is, e.g., 100 sccm according to the embodiment). Specifically,the processing gas G3 is supplied from the selected gas source of aplurality of gas sources of the gas source 122 into the processingcontainer 192. In addition, a high frequency power (e.g., 60 MHz and 600W according to the embodiment) is supplied from the high-frequency powersource 150A and the high-frequency power source 150B, and the exhaustdevice 50 is operated to set the pressure of the processing space Sp inthe processing container 192 to a preset value (e.g., 400 mTorraccording to the embodiment). In this manner, the plasma of theprocessing gas G3 is generated in the processing container 192. Theexecution time of the step ST2 a is, for example, 400 to 600 s accordingto the embodiment.

The set value of the pressure of the processing space Sp in the step ST2(especially, the step ST2 a) is relatively high (200 mTorr or more) asillustrated in FIG. 6, and may be, for example, 400 mTorr according tothe embodiment. When the pressure of the processing space Sp isrelatively high in this way, the ions of the nitrogen atom included inthe plasma of the processing gas G3 (hereinafter, referred to as anitrogen ion) are isotropically brought into contact with the surface ofthe film LA so that the surface of the film LA is isotropically anduniformly modified by the nitrogen ions. Thus, the mixed layer MX havinga uniform (substantially uniform) thickness is also formed on thesurface of the film LA as illustrated in FIG. 8. FIG. 8 is across-sectional view illustrating the state of the wafer W after surfacemodification in the method illustrated in FIG. 7.

In the step ST2 a, the plasma of the processing gas G3 is generatedwithin the processing container 192 in this manner, and the nitrogenions included in the plasma of the processing gas G3 are brought intocontact with the surface of the film LA by drawing the ions by the highfrequency bias power in the vertical direction (the direction toward thesurface of the wafer W placed on the electrostatic chuck ESC from theceiling side of the processing container 192 (specifically, e.g., theplate-like dielectric 194), so that the surface of the film LA isisotropically and uniformly modified. In this manner, the surface of thefilm LA in the step ST2 a becomes a mixed layer MX having a uniformthickness (substantially the same thickness) over the surface of thewafer W. Since the processing gas G3 includes nitrogen and the film LAincludes silicon oxide (e.g., SiO₂ according to the embodiment), thecomposition of the mixed layer MX may be, for example, SiN/SiO₂ (SiON)according to the embodiment.

The processing time in the step ST2 a is longer than the time requiredto reach the self-control area of the ALE method. FIG. 9 illustrates theself-controllability of surface modification in the sequence SQ2 (inparticular, the step ST2 a) illustrated in FIG. 7. The horizontal axisin FIG. 9 represents the processing time (s) of the surface modification(more specifically, the processing performed in the step ST2 a), and thevertical axis in FIG. 9 represents the etching amount (nm) (thethickness of which the portion is surface modified by the step ST2 a).The result illustrated in FIG. 9 is a result obtained by executing thestep ST2 a in which the pressure of the processing space Sp is set to400 mTorr, the value of the high frequency power is set to 600 W, andthe value of the high-frequency bias power is set to 50 W. Asillustrated in FIG. 9, the surface modification performed by the stepST2 a involves self-controllability. That is, when the surfacemodification is performed over the time taken to reach the self-controlarea of the ALE method, the surface modification is isotropically anduniformly performed regardless of the hole width and the hole density,and thus, an isotropic and uniform mixed layer MX may be formed in thesame manner on the surface of the wafer W (the inner surface of thesurface MK1 of the mask MK, and the inner surface of the trench of themask MK (including the holes HL1 and HL2)).

FIGS. 10A to 10C are views illustrating the principle of etching in thestep illustrated in FIG. 8. In FIGS. 10A to 10C, a blank circle (whitecircle) represents an atom constituting the film LA (atoms constitutingSiO₂ according to the embodiment), a black circle represents thenitrogen ion included in the plasma of the processing gas G3, and acircled “x” represents the radicals included in the plasma of theprocessing gas G4, which will be described later. As illustrated in FIG.10A, the nitrogen ions included in the plasma of the processing gas G3(black circles) are isotropically supplied to the atomic layer on thesurface of the film LA by the step ST2 a. In this manner, a mixed layerMX that includes atoms constituting the film LA and nitrogen atoms ofthe processing gas G3 is formed in the atomic layer on the surface ofthe film LA by the step ST2 a.

As described above, since the processing gas G3 includes nitrogen,nitrogen atoms are supplied to the atomic layer on the surface of thefilm LA (the atomic layer of the silicon oxide) in the step ST2 a, sothat the mixed layer MX containing the silicon nitride (e.g., SiN/SiO₂according to the embodiment) may be formed in the atomic layer on thesurface of the film LA.

The processing space Sp in the processing container 192 is purged in thestep ST2 b following the step ST2 a. Specifically, the processing gas G3supplied in the step ST2 b is exhausted. In the step ST2 b, an inert gassuch as a rare gas (e.g., Ar gas according to the embodiment) may besupplied as a purge gas to the processing container 192. That is, thepurging of the step ST2 b may be either gas purging for causing an inertgas to flow into the processing container 192 or purging by vacuuming.

In the step ST2 c following the step ST2 b, the plasma of the processinggas G4 (second gas) is generated in the processing container 192, andthe entire mixed layer MX is removed by chemical etching using theradicals included in the plasma. Thus, the film LA may be etchedisotropically and uniformly over the surface of the wafer W(particularly, the film LA provided on the inner surfaces of all theholes). In the step ST2 c, the processing gas G4 is supplied into theprocessing container 192 to generate the plasma of the processing gas G4at a state where the wafer W after the formation of the mixed layer MXin the step ST2 a is placed on the electrostatic chuck ESC. The plasmaof the processing gas G4 generated in the step ST2 c includes radicalsthat remove the mixed layer MX including the silicon nitride. Theprocessing gas G4 includes fluorine and may be a mixed gas thatincludes, for example, NF₃ gas and O₂ gas according to the embodiment.The processing gas G4 may be a mixed gas including NF₃ gas, O₂ gas, H₂gas, and Ar gas, a mixed gas including CH₃F gas, O₂ gas, and Ar gas, orthe like. Specifically, the processing gas G4 is supplied from theselected gas sources of a plurality of gas sources of the gas source 122to the processing container 192, the high frequency power is suppliedfrom the high-frequency power source 150A and the high-frequency powersource 150B (e.g., 60 MHz and 600 W according to the embodiment), andthe pressure of the processing space Sp in the processing container 192is set to a preset value (e.g., 400 mTorr according to the embodiment)by operating the exhaust device 50. In this manner, the plasma of theprocessing gas G4 is generated in the processing container 192. Theexecution time of the step ST2 c is, for example, 400 to 600 s accordingto the embodiment.

As illustrated in FIG. 10B, the radicals in the plasma of the processinggas G4 generated in the step ST2 c (“x” surrounded by a circle in FIG.10B) are brought into contact with the mixed layer MX on the surface ofthe film LA, and the radicals of atoms of the processing gas G4 aresupplied to the mixed layer MX formed on the surface of the film LA sothat the mixed layer MX may be removed from the film LA by chemicaletching. As illustrated in FIG. 10C, the entire mixed layer MX formed onthe surface of the film LA in the step ST2 c may be removed from thesurface of the film LA by the radical included in the plasma of theprocessing gas G4. By removing the mixed layer MX, the hole width isisotropically and uniformly increased over the surface of the wafer W,regardless of the hole width and the hole density.

The processing space Sp in the processing container 192 is purged in thestep ST2 d following the step ST2 c. Specifically, the processing gas G4supplied in the step ST2 d is exhausted. In the step ST2 d, an inert gassuch as a rare gas (e.g., Ar gas according to the embodiment) may besupplied as a purge gas to the processing container 192. That is, thepurging of the step ST2 d may be either gas purging for causing an inertgas to flow into the processing container 192 or purging by vacuuming.

It is determined whether the execution of the sequence SQ2 is terminatedin the step ST2 e following the sequence SQ2. Specifically, in the stepST2 e, it is determined whether the number of executions of the sequenceSQ2 reaches a predetermined number. Determination of the number ofexecutions of the sequence SQ2 is to determine the etching amount forthe film LA. The sequence SQ2 may be repeatedly performed so that thefilm LA is etched until the etching amount for the film LA reaches apreset value. As the number of executions of the sequence SQ2 increases,the etching amount for the film LA also increases (increasessubstantially linearly). Therefore, the number of executions of thesequence SQ2 may be determined so that the product of the thickness ofthe film LA (the thickness of the mixed layer MX formed in the step ST2e that is performed once), which is etched by the execution of thesequence SQ2 performed once (unit cycle), and the number of executionsof the sequence SQ2 becomes a preset value.

With reference to FIG. 11, descriptions will be made on the change inthe etching amount with respect to the film LA generated during theexecution of the sequence SQ2 and the change in the thickness of themixed layer MX formed in the film LA. A line GL1 in FIG. 11 representsthe change in the etching amount (arbitrary unit) with respect to thefilm LA occurring during the execution of the sequence SQ2, and a lineGL2 in FIG. 11 represents the change in the thickness of the mixed layerMX (arbitrary unit) occurring during the execution of the sequence SQ2.The horizontal axis in FIG. 11 represents the time during which thesequence SQ2 is executed, but the execution time in the step ST2 b andthe execution time in the step ST2 d are omitted for the sake ofsimplicity. As illustrated in FIG. 11, in the execution of the sequenceSQ2 performed once (unit cycle), the execution of the step ST2 a isperformed until the thickness of the mixed layer MX reaches a presetvalue TW, as indicated by the line GL2. The value TW of the thickness ofthe mixed layer MX formed in the step ST2 a may be determined by thevalue of the bias power applied by the high-frequency power source 64,the dose per unit time for the film LA of the nitrogen ion included inthe plasma of the processing gas G3, and the execution time of the stepST2 c.

As illustrated in FIG. 11, in the execution of the sequence SQ2performed once (unit cycle), the execution of the step ST2 c isperformed until the entire mixed layer MX formed in the step ST2 a isremoved as indicated by the lines GL1 and GL2. The entire mixed layer MXis removed by chemical etching until a timing TI is reached during theexecution of the step ST2 c. The timing TI may be determined by theetching rate of the chemical etching performed in the step ST2 c. Thetiming TI occurs during the execution of the step ST2 c. During theperiod from the timing TI to the end of the step ST2 c, the film LA ofthe silicon oxide after removal of the mixed layer MX is not etched bythe plasma of the processing gas G4. That is, when the radicals includedin the plasma of the processing gas G4 are used, the etching rate of theetching for the silicon oxide (e.g., SiO₂) constituting the film LA isextremely small compared to the etching rate of the etching for thesilicon nitride (e.g., SiN) included in the mixed layer MX.

When it is determined in the step ST2 e that the number of executions ofthe sequence SQ2 has not reached the preset number (“NO” in the step ST2e), the execution of the sequence SQ2 is repeated again. In themeantime, when it is determined in the step ST2 e that the number ofexecutions of the sequence SQ2 has reached the preset number (“YES” inthe step ST2 e), the step ST2 ends and proceeds to the step ST3illustrated in FIG. 1.

As described above, a series of isotropic etching processes of thesequence SQ2 and the process ST2 e may remove the surface of the film LAfor each atomic layer by the same method as the ALE method. Therefore, aseries of isotropic etching processes of the sequence SQ2 and the stepST2 e may be performed by repeatedly executing the sequence SQ2 so as toremove the surface of the film LA for each atomic layer, thereby etchingthe film LA isotropically and precisely regardless of the hole width andthe hole density. That is, since the sequence SQ2 is repeated apredetermined number of times, the film LA is isotropically andprecisely etched at an isotropic and uniform thickness (approximatelythe same thickness) over the entire surface of the wafer W, regardlessof the hole width and the hole density.

<Modification of Step ST1>

Subsequently, another embodiment of the step ST1 (modification) will bedescribed. The film LA illustrated in FIG. 4 is one layer, but may be atwo layer without being limited thereto. FIG. 12 is a cross-sectionalview illustrating the state of the wafer W after a two-layered film isformed in the film forming step illustrated in FIG. 1. The film LAillustrated in FIG. 12 includes a two-layered film, and also includes afilm LA1 (first film) and a film LA2 (second film). The film LA1 isformed on the surface of the wafer W (the surface MK1 of the mask MK(including the inner surface of the hole)), and the film LA2 is formedon the surface of the film LA1. The film LA1 in the hole HL1 has a filmthickness WF2 a, and the film LA2 in the hole HL1 has a film thicknessWF3 a. The film LA1 in the hole HL2 has a film thickness WF2 b, and thefilm LA2 in the hole HL2 has a film thickness WF3 b. Since the holewidth WW1 a of the hole HL1 is narrower than the hole width WW1 b of thehole HL2, the film thickness WF2 a is thinner than the film thicknessWF2 b and the film thickness WF3 a is thinner than the film thicknessWF3 b. The film LA1 and the film LA2 include a silicon oxide and mayinclude, for example, SiO₂ according to the embodiment. The oxygencontent of the film LA2 is higher than the oxygen content of the filmLA1. The etching resistance of the film LA1 performed in the step ST2 islower in the film LA1 than the film LA2. That is, the value of theetching rate (nm/min) of the film LA1 for the etching performed in thestep ST2 is greater than the value of the etching rate (nm/min) of thefilm LA2 for the etching performed in the step ST2.

The step ST1 according to the modification will be described withreference to FIG. 13. The step ST1 illustrated in FIG. 13 includes thestep ST1 a (seventh step) and the step ST1 b (eighth step). In the stepST1 a, the film LA1 is formed on the inner surface of the hole. In thestep ST1 b, the film LA2 is formed on the film LA1. According to theembodiment, for example, in the step ST1 a, the film LA1 having arelatively low etching resistance with respect to the etching performedin the step ST2 is formed by a plasma CVD method, and in the step ST1 b,the film LA2 having a relatively high etching resistance with respect tothe etching performed in the step ST2 is formed by the plasma CVDmethod. That is, according to the embodiment, the film LA1 is formedusing the plasma CVD method in the step ST1 a, and the film LA2 isformed using the plasma CVD method in the step ST1 b.

The etching resistance of the silicon oxide film may be changed by theflow rate of the O₂ gas added at the time of film formation. FIG. 14 isa view illustrating a correlation between the amount of oxygen addedduring film formation and the etching resistance of the film. Thehorizontal axis in FIG. 14 represents the flow rate (sccm) of O₂ gasthat may be added during the film formation, and the vertical axis inFIG. 14 represents the etching rate (nm/min) indicating the etchingresistance of the film. The result indicated by a line GE1 in FIG. 14 isobtained by using, as film forming conditions, a pressure of 10 mTorr, ahigh frequency power of 60 MHz and 1000 W by the high-frequency powersource 150A and the high-frequency power source 150B, a mixed gas ofSiCl₄ (25 sccm), He (100 sccm), and O₂ (0 to 100 sccm), and a processingtime of 60 s, and by using, as etching conditions, a pressure of 20mTorr, a high frequency power of 60 MHz and 500 W by the high-frequencypower source 150A and the high-frequency power source 150B, a highfrequency power of 40 MHz and 50 W by the high-frequency power source64, Cl₂ gas (200 sccm), and a processing time of 60 s. The resultindicated by a line GE2 in FIG. 14 is obtained by using, as etchingconditions, a pressure of 20 mTorr, a high frequency power of 60 MHz and500 W by the high-frequency power source 150A and the high-frequencypower source 150B, a high frequency power of 40 MHz and 100 W by thehigh-frequency power source 64, a mixed gas of C₄F₈ (40 sccm) and Ar(200 sccm), and a processing time of 60 s. As illustrated in FIG. 14, itis possible to change the etching resistance of the silicon oxide filmby adjusting the amount of oxygen added (the flow rate of O₂ gas). Asthe amount of oxygen added decreases, the etching rate increases. Forexample, in FIG. 14, the selection ratio of the etching may becontrolled within the range of 1 to 17 by adjusting the amount of oxygenadded.

FIG. 13 is referred back to again. In the step ST1 a, a processing gasG5 is supplied to the processing container 192 to generate plasma of theprocessing gas G5 at a state where the wafer W is placed on theelectrostatic chuck ESC. The processing gas G5 contains a gas specieshaving a superior deposition property and contains, for example, siliconaccording to the embodiment. The processing gas G5 is a mixed gas ofSiCl₄, He, and O₂ (according to embodiment, the gas flow rates are 25sccm (SiCl₄), 100 sccm (He), and 0 to 5 sccm (O₂), respectively), or thelike. The O₂ gas included in the processing gas G5 is about 0 to severalsccm (according to embodiment, about 0 to 5 sccm), which is relativelysmall. The processing gas G5 is supplied from the selected gas source ofa plurality of gas sources of the gas supply source 122 into theprocessing container 192. A high frequency power (e.g., 60 MHz and 1000W according to the embodiment) is supplied from the high-frequency powersource 150A and the high-frequency power source 150B, and the exhaustdevice 50 is operated to set the pressure of the processing space Sp inthe processing container 192 to a preset value (e.g., 10 mTorr accordingto the embodiment). The execution time of the step ST1 a is, forexample, 60 s according to the embodiment. Since the processing gas G5contains a gas species having a superior deposition property, asillustrated in FIG. 12, the film thickness of the film LA1 formed by thestep ST1 a is relatively thin with respect to the inner surface of thehole HL1 having a relatively narrow hole width and is relatively thickwith respect to the inner surface of the hole HL2 having a relativelywide hole width. That is, the value of the film thickness WF2 a of thefilm LA1 formed on the inner surface of the hole HL1 is smaller than thefilm thickness WF2 b of the film LA1 formed on the inner surface of thehole HL2.

In the step ST1 b following the step ST1 a, a processing gas G6 issupplied into the processing container 192 to generate plasma of theprocessing gas G6 while the wafer W is placed on the electrostatic chuckESC. The processing gas G6 contains a gas species having a superiordeposition property and contains, for example, silicon according to theembodiment. According to the embodiment, the processing gas G6 may be amixed gas of SiCl₄, He, and O₂ (according to the embodiment, the gasflow rates are 25 sccm (SiCl₄), 100 sccm (He), 100 sccm (O₂),respectively), or the like. The O₂ gas included in the processing gas G6is about 100 sccm according to the embodiment, which is relativelylarge. The processing gas G6 is supplied from the selected gas source ofa plurality of gas sources of the gas supply source 122 into theprocessing container 192. A high frequency power (e.g., 60 MHz and 1000W according to the embodiment) is supplied from the high-frequency powersource 150A and the high-frequency power source 150B, and the exhaustdevice 50 is operated to set the pressure of the processing space Sp inthe processing container 192 to a preset value (e.g., 10 mTorr accordingto the embodiment). The execution time of the step ST1 b is, forexample, 60 s according to the embodiment. Since the processing gas G6contains a gas species having a superior deposition property, asillustrated in FIG. 12, the film thickness of the film LA2 formed by thestep ST1 b is relatively thin with respect to the inner surface of thehole HL1 having a relatively narrow hole width and is relatively thickwith respect to the inner surface of the hole HL2 having a relativelywide hole width. That is, the value of the film thickness WF3 a of thefilm LA2 formed on the inner surface of the hole HL1 is smaller than thefilm thickness WF3 a of the film LA2 formed on the inner surface of thehole HL2.

With reference to FIG. 15, descriptions will be made on the change inthe hole width that may occur when the method MT includes the step ST1illustrated in FIG. 13 (the step of forming a two-layered film (the filmLA1 and the film LA2)). FIG. 15 is a view schematically illustrating thechange in the hole width that may occur when the film forming stepillustrated in FIG. 1 forms the two-layered film and the sequenceillustrated in FIG. 1 is repeatedly executed. The line G1 a representsthe change in the hole width of the hole HL1, and the line G2 brepresents the change in the hole width of the hole HL2.

The step ST1 includes a step represented by a section V11 and a steprepresented by a section V12. The section V11 represents the step ST1 ain which the film LA1 is formed, and the section V12 represents the stepST1 b in which the film LA2 is formed. The film LA1 having a relativelylow etching resistance is formed in the section V11 and the film LA2having a relatively high etching resistance is formed in the section V12following the section V11. When the film LA is formed in the step ST1,the film LA is relatively thin in the hole HL1 having a relativelynarrow hole width, and the film LA is relatively thick in the hole HL2having a relatively wide hole width. Thus, the difference between thehole width at the hole HL2 and the hole width at the hole HL1(difference H2 b) at the end of the step ST1 is smaller than thedifference at the start of the step ST1 (difference H1 b).

Isotropic etching is performed in the step ST2 following the step ST1.The step ST2 includes a step represented by a section V21, a steprepresented by a section V22, and a step represented by a section V23.The section V21 represents the step from the start of the step ST2 untilthe entire film LA2 in the hole HL1 is removed by etching. In thesection V21, the film LA2 having a relatively high etching resistance isetched in any of the holes HL1 and HL2. Since the film thickness WF3 aof the film LA2 in the hole HL1 is thinner than the film thickness WF3 bof the film LA2 in the hole HL2, the film LA2 in the hole HL1 is removedby etching earlier than the film LA2 in the hole HL2. At the end of thesection V21, the entire film LA2 in the hole HL1 is removed by etching,but a portion of the film LA2 in the hole HL2 remains. In the sectionV21, isotropic etching is performed on the film LA2 in any of the holesHL1 and HL2, so that the difference in the hole width between the holeHL2 and the hole HL1 (difference H2 b) is maintained constant and thefilm LA2 is etched. Therefore, the difference between the hole width ofthe hole HL2 and the hole width of the hole HL1 at the end of thesection V21 is maintained as the difference H2 b as at the start of thesection V21.

The section V22 following the section V21 is removed after the entirefilm LA2 in the hole HL2 is removed by etching (from the end of thesection V21) until the entire film LA2 in the hole HL2 is removed byetching (until the entire film LA2 is removed from the surface of thewafer W). In the section V22, since the film LA2 having a relativelyhigh etching resistance is continuously etched in the hole HL2, and thefilm LA1 having a relatively low etching resistance is etched in thehole HL1, so that the etching in the hole HL1 is performed more quicklythan the etching in the hole HL2. The entire film LA2 in the hole HL2has been removed by etching at the end of the section V22. Therefore, inthe section V22, the difference in the hole width between the hole HL2and the hole HL1 becomes smaller with the progress of the etching. Also,the difference in the hole width between the hole HL2 and the hole HL1at the end of the section V22 (difference H3 b) is smaller than thedifference in the hole width between the hole HL2 and the hole HL1 atthe start of the section V22 (difference H2 b).

The section V23 following the section V22 indicates the step in whichthe film LA1 is etched in the holes HL1 and HL2. Since the film LA1 isisotropically etched in any of the holes HL1 and HL2 in the section V22,the difference in the hole width between the hole HL2 and the hole HL1(difference H3 b) is maintained constant, while the film LA1 is etched.Therefore, the difference in the hole width between the hole HL2 and thehole HL1 at the end of the section V23 is maintained as the differenceH3 b as at the start of the section V23.

Descriptions will be made on the improvement of the variation in thehole width by executing the sequence SQ1 once using the step ST1illustrated in FIG. 13. In the hole HL1, the film thickness WF2 a of thefilm LA1 is denoted by K11, and the film thickness WF3 a of the film LA2is denoted by K12. In the hole HL2, the film thickness WF2 b of the filmLA1 is denoted by K21, and the film thickness WF3 b of the film LA2 isdenoted by K22. In the etching of the step ST2, it is assumed that thevalue of the etching rate of the film LA1 is R1 and the value of theetching rate of the film LA2 is R2. At the end point of the section V22illustrated in FIG. 15 (at the time when the entire film LA2 is removedfrom the surface of the wafer W), the difference in the film thicknessbetween the film LA2 formed on the inner surface of the hole HL2 and thefilm LA2 formed on the inner surface of the hole HL1 becomesK21−(K11−(R1/R2)×(K22−K12)). Therefore, the improvement amount of thelocal CD uniformity (LCDU) is (K21−K11)+(R1/R2)×(K22−K12). Since R1>R2,R1/R2>1. Thus, the above-described improvement amount becomes a valuethat is larger than the value obtained by simply adding the differencebetween the film thickness WF2 b of the film LA1 in the hole HL2 and thefilm thickness WF2 a of the film LA1 in the hole HL1 (K21−K11), and thedifference between the film thickness WF3 b of the film LA2 in the holeHL1 and the film thickness WF3 a of the film LA2 in the hole HL1(K21−K11). Therefore, an effective improvement against the reduction ofthe hole width variation is expected.

Further, when the value of the difference H1 b illustrated in FIG. 15(the value obtained by subtracting the value of the hole width WW1 a inthe hole HL1 before formation of the film LA from the value of the holewidth WW1 b in the hole HL2 before formation of the film LA) is assumedto be Δ, the value of the difference H3 b illustrated in FIG. 15 becomesΔ−2×(K21−K11)−2×(R1/R2)×(K22−K12). Therefore, the difference in the holewidth between the holes HL1 and HL2 after the execution of the sequenceSQ1 is reduced by the hole width difference Δ1 of 2×(K21−K11)2×(R1/R2)×(K22−K12) than the hole width difference Δ between the holesHL1 and HL2 before the execution of the sequence SQL Since Δ1 is largerthan the value in a case where R1=R2, that is, the value in a case wherethe film LA is only a single layer, (2×(K21−K11)+2×(K22−K12)), when thestep ST1 according to the modification (when the film LA includes twolayers of the film LA1 and the film LA2) is used, the reduction of thevariation in the hole width may be more effectively implemented by theexecution of the sequence SQ1.

In the meantime, a step of forming a film LA that has two layers havingdifferent amounts of oxygen added (films LA1 and LA2) as illustrated inFIG. 12 has been exemplified as a step of forming the film LA having twolayers (the modification of the step ST1). However, the presentdisclosure is not limited to this and may be configured such that two ormore films such as, for example, a silicon-containing film, aboron-containing film, a metal film, and a carbon film are combined tohave the same effect as the film LA having the film LA1 and the filmLA2.

Further, although the plasma CVD method is used to form the film LA1 inthe step ST1 a, it is also possible to form the film LA1 on the surfaceof the wafer W (in particular, on the inner surface of the hole) in aconformal manner by the same method as the atomic layer deposition (ALD)method without being limited thereto. A method of forming the film LA1by the same method as the ALD method in the step ST1 a will be describedwith reference to FIG. 16 and FIGS. 17A to 17C. FIG. 16 is a flow chartillustrating another example of the step ST1 a among the film formingsteps illustrated in FIG. 13. FIGS. 17A to 17C are diagrams illustratingthe principle of formation of the film LA1 in the step illustrated inFIG. 16.

The step ST1 a includes a sequence SQ3 (third sequence) and a step ST1ae. A series of steps including the sequence SQ3 and the step ST1 aeforms a film (film LA1) on the surface of the wafer W carried into theprocessing container 192 (the surface MK1 of the mask MK and the innersurface of the hole of the mask MK). The sequence SQ3 includes a stepST1 aa (ninth step), a step ST1 ab (tenth step), a step ST1 ac (eleventhstep), and a step ST1 ad (twelfth step). In the step ST1 aa, aprocessing gas G7 (third gas) is supplied into the processing container192. Specifically, in the step ST1 aa, the processing gas G7 containingsilicon is introduced into the processing container 192 as illustratedin FIG. 17A.

The processing gas G7 includes an organic group-containingaminosilane-based gas. As the processing gas G7, an aminosilane-basedgas having a molecular structure having a relatively small number ofamino groups may be used, and for example, monoaminosilane (H₃—Si—Rwhere R is an amino group which contains an organic group and may besubstituted) may be used. Further, the aminosilane-based gas used as theprocessing gas G7 may include aminosilane having 1 to 3 silicon atoms oraminosilane having 1 to 3 amino groups. The aminosilane having 1 to 3silicon atoms may be monosilane having 1 to 3 amino groups(monoaminosilane), disilane having 1 to 3 amino groups, or trisilanehaving 1 to 3 amino groups. In addition, the aminosilane may have anamino group which may be substituted. The amino groups may besubstituted by any of methyl, ethyl, propyl, and butyl groups. Further,the methyl, ethyl, propyl, or butyl group may be substituted by halogen.The processing gas G7 of the organic group-containing aminosilane-basedgas from the selected gas source of a plurality of gas sources of thegas supply source 122 is supplied into the processing container 192. Theprocessing time in the step ST1 aa is longer than the time taken toreach the self-control area of the ALD method.

The molecules of the processing gas G7 are attached to the surface ofthe wafer W (the surface MK1 of the mask MK and the inner surface of thehole of the mask MK) as a reaction precursor (layer Ly1) as illustratedin FIG. 17B. In the step ST1 aa, the plasma of the processing gas G7 isnot generated. The molecules of the processing gas G7 are attached tothe surface of the wafer W by chemical adsorption based on chemicalbonding, and no plasma is used. When the processing gas G7 may beattached to the surface of the wafer W by chemical bonding and containssilicon, such a gas may be used.

In the meantime, monoaminosilane is selected, for example, as theprocessing gas G7, because monoaminosilane has a relatively highelectrical negativity and a polar molecular structure so that chemicaladsorption may be performed relatively easily. A layer Ly1 of a reactionprecursor formed by attaching the molecules of the processing gas G7 tothe surface of the wafer W is in a state of being close to amonomolecular layer (monolayer) because the attachment is chemicaladsorption. As the amino group (R) of the monoaminosilane becomessmaller, the molecular structure of the molecule attached to the surfaceof the wafer W becomes smaller, so that the steric hindrance caused bythe molecular size is reduced. Thus, the molecules of the processing gasG7 may be uniformly attached to the surface of the wafer W, and thelayer Ly1 may be formed with a uniform film thickness on the surface ofthe wafer W.

As described above, since the processing gas G7 contains an organicgroup-containing aminosilane-based gas, the reaction precursor ofsilicon (layer Ly1) is formed along the atomic layer on the surface ofthe wafer W by the step ST1 aa.

In the step ST1 ab following the step ST1 aa, the processing space Sp inthe processing container 192 is purged. Specifically, the processing gasG7 supplied in the step ST1 aa is exhausted. In the step ST1 ab, aninert gas such as a nitrogen gas or a rare gas (e.g., Ar) may besupplied as a purge gas into the processing container 192. That is, thepurging of the step ST1 ab may be either gas purging for causing aninert gas to flow into the processing container 192 or purging byvacuuming. In the step ST1 ab, the molecules attached in an excessiveamount to the surface of the wafer W may also be removed. Thus, thelayer Ly1 of the reaction precursor becomes an extremely thin molecularlayer formed on the surface of the wafer W.

In the step ST1 ac following the step ST1 ab, as illustrated in FIG.17B, plasma P1 of a processing gas G8 (fourth gas) is generated in theprocessing space Sp of the processing container 192. The processing gasG8 includes a gas containing an oxygen atom, and may include, forexample, an oxygen gas. The processing gas G8 including the gascontaining an oxygen atom is supplied from the selected gas source of aplurality of gas sources of the gas supply source 122 into theprocessing container 192. Then, a high frequency power is supplied fromthe high-frequency power source 150A and the high-frequency power source150B. The pressure of the processing space Sp in the processingcontainer 192 is set to a preset pressure by operating the exhaustdevice 50. In this manner, the plasma P1 of the processing gas G8 isgenerated in the processing space Sp.

As illustrated in FIG. 17B, when the plasma P1 of the processing gas G8is generated, an active species of oxygen, for example, an oxygenradical, is generated. Further, as illustrated in FIG. 17C, a layer Ly2which is a silicon oxide film (a layer included in the film LA1illustrated in FIG. 12) is formed as an extremely thin molecular layer.

As described above, since the processing gas G8 includes oxygen atoms,the oxygen atom are bonded to the reaction precursor of the silicon(layer Ly1) formed on the surface of the wafer W in the step ST1 ac, sothat the layer Ly2 of a silicon oxide film may be formed on the surfaceof the wafer W. Therefore, in the sequence SQ3, the layer Ly2 of thesilicon oxide film may be formed on the surface of the wafer W by thesame method as the ALD method.

The processing space Sp in the processing container 192 is purged in thestep ST1 ad following the step ST1 ac. Specifically, the processing gasG8 supplied in the step ST1 ac is exhausted. In the step ST1 ad, aninert gas such as a nitrogen gas or a rare gas (e.g., Ar) may besupplied as a purge gas into the processing container 192. That is, thepurging of the step ST1 ad may be either gas purging for causing aninert gas to flow into the processing container 192 or purging byvacuuming.

In the step ST1 ae following the sequence SQ3, it is determined whetherthe number of repetitions of the sequence SQ3 has reached a presetnumber. When it is determined that the number of repetitions has notbeen reached (“NO” in the step ST1 ae), the sequence SQ3 is executedagain. When it is determined that the number of repetitions has beenreached (“YES” in the step ST1 ae), the process proceeds to the step ST1b. That is, in the step ST1 ae, the execution of the sequence SQ3 isrepeated to form the film LA1 on the surface of the wafer W until thenumber of repetitions of the sequence SQ3 reaches the preset number. Thenumber of repetitions of the sequence SQ3 controlled by the step ST1 aeis set so that a hole having the smallest hole width among a pluralityof holes formed on the surface of the wafer W has a larger hole widththan the preset reference width, without being occluded by the film LA1formed by the sequence SQ3 or the like (furthermore, the film LA2 formedby the step ST1 b) (while at least the hole opening is not occluded).

In this manner, when the film LA1 is formed in a conformal manner by thesame method as the ALD method in the step ST1 a, the film LA1 is formedin a conformal manner on the surface of the wafer W (especially, on theinner surface of the hole) by repeatedly executing the sequence SQ3 thatincludes: the step ST1 aa of first forming a reaction precursorcontaining silicon (layer Ly1) on the surface of the wafer W(especially, the inner surface of the hole) using an aminosilane-basedgas without using plasma; and the step ST1 ac of forming a thin filmcontaining a silicon oxide (layer Ly2) by bonding an oxygen atom to thereaction precursor using the plasma of a gas containing an oxygen atom.

As described above, in the method MT according to the embodiment, thestep ST1 includes a film forming process using the plasma CVD method.Therefore, the film LA having a relatively thin film thickness is formedwith respect to the hole HL1 having a relatively narrow hole width andthe film LA having a relatively thick film thickness is formed withrespect to the hole HL2 having a relatively wide hole width. Therefore,even when the hole width varies in a plurality of holes, the variationmay be reduced by the film forming process in the step ST1. Further,since the film LA formed by the step ST1 is isotropically etched in thestep ST2, the film LA formed in the step ST1 may cause the hole width tobe adjusted while maintaining the hole width reduced.

In addition, since the sequence SQ1 is executed repeatedly, the filmhaving the finally desired film thickness may be formed by forming thefilm having a relatively thin film thickness (a film included in thefilm LA) in the step ST1, and repeatedly executing the sequence SQ1.Thus, it is possible to sufficiently avoid the situation that theopening of the hole HL1 is occluded by the film formed by the step ST1in the hole HL1 having a relatively narrow hole width.

The surface of the film LA formed in the step ST1 is isotropicallymodified by the method similar to the ALE method as in the step ST2illustrated in FIG. 7, and a mixed layer MX is entirely removed afterthe mixed layer MX is isotropically formed on the surface of the film.Thus, the film LA formed in the step ST1 may be isotropically anduniformly removed by the etching performed in the step ST2.

Even when the film LA2 is removed in the step ST2 in the hole HL1 inwhich a relative thin film is formed in the step ST1 due to a relativelynarrow hole width, a portion of the film LA2 may remain in the hole HL2in which a relatively thick film is formed in the step ST1 due to arelatively wide hole width. When etching is continuously performed inthe step ST2 from this state, the etching resistance of the film LA1 islower than the etching resistance of the film LA2, so that the etchingof the hole HL1 is performed faster than that of the hole HL2.Therefore, the variation in the hole width between the hole HL1 and thehole HL2 may be more effectively reduced using the film LA1 having arelatively low etching resistance and the film LA2 having a relativelyhigh etching resistance.

Since the film LA1 is formed by the same method as the ALD method as inthe step ST1 a illustrated in FIG. 16, the film LA1 having a relativelythin film thickness may be formed in a conformal manner in the step ST1a. Therefore, even when the film LA2 is formed by the plasma CVD method,the entire film thickness of the film LA including the film LA1 and thefilm LA2 may be effectively controlled.

In the above embodiment, the films LA1 and LA2 are described assilicon-containing films. However, the present disclosure is not limitedthereto. The films LA1 and LA2 are films other than thesilicon-containing films, and may be formed by the plasma CVD on theinner surface of the hole and may be etched isotropically. Further, theetching resistance for the etching performed in the step ST2 may belower in the film LA1 than the film LA2. For example, the films LA1 andLA2 may be any of a silicon-containing film, a boron-containing film, ametal film, and a carbon-containing film.

From the foregoing, it will be appreciated that various exemplaryembodiments of the present disclosure have been described herein forpurposes of illustration, and that various modifications may be madewithout departing from the scope and spirit of the present disclosure.Accordingly, the various exemplary embodiments disclosed herein are notintended to be limiting, with the true scope and spirit being indicatedby the following claims.

What is claimed is:
 1. A method of processing a workpiece, the methodcomprising: providing a workpiece formed with a plurality of holes on asurface thereof in a processing container of a plasma processingapparatus, the plurality of holes including a small diameter hole and alarge diameter hole having a diameter larger than the small diameterhole, and the workpiece having an initial size difference which is adifference between a first diameter of the large diameter hole and asecond diameter of the small diameter hole, the workpiece furtherincluding a processing target layer positioned below the plurality ofholes; performing a first sequence on the workpiece including: a firstprocess of forming a film on a sidewall of an inner surface of each ofthe plurality of holes by a plasma CVD, a thickness of the film formedon the inner surface of the small diameter hole being smaller than athickness of the film formed on the inner surface of the large diameterhole, with the thicknesses each being in a direction extending away fromeach of the sidewalls; a second process of isotropically etching thefilm such that the small diameter hole is etched to a small hole filminner diameter and the large diameter hole is etched to a large holefilm inner diameter, wherein during the second process the thicknessesof the film on the sidewalls of the plurality of holes are reduced bythe isotopically etching, wherein the workpiece has a post-etch sizedifference which is a difference between the large hole film innerdiameter and the small hole film inner diameter, and the post-etch sizedifference is smaller than the initial size difference, and after the atleast one first sequence including the first process and the secondprocess, performing a third process in which the processing target layeris etched through the plurality of holes.
 2. The method of claim 1,further comprising repeating the first process and the second process ofthe first sequence, and after the repeating, performing the thirdprocess.
 3. The method of claim 1, further comprising repeating thefirst process and the second process of the first sequence, wherein thepost-etch size difference is smaller than the initial size differencesuch that size differences between the large hole film inner diameterand the small hole film inner diameter progressively become smaller asthe first sequence is repeated.
 4. The method of claim 1, wherein theworkpiece includes a mask disposed on the processing target layer, andthe plurality of holes are formed in the mask.
 5. The method of claim 1,wherein the film formed on the sidewall of the inner surface of each ofthe plurality of holes includes carbon.
 6. The method of claim 1,wherein the first process of forming forms a first film on the innersurface of the holes, and a second film on the first film, and anetching resistance of the first film is lower than an etching resistanceof the second film in the second process of isotropically etching. 7.The method of claim 6, further including, during the isotropicallyetching, etching through the second film of small diameter hole toexpose the first film while the second film of the large diameter holecontinues to cover the first film of the large diameter hole; and afterexposing the first film in the small diameter hole, continuing theisotropically etching to etch the first film in the small diameter holeand to etch the second film in the large diameter hole, and during thecontinuing of the isotropically etching an amount of decrease inthickness of the first film in the small diameter hole is larger than anamount of decrease in thickness in the second film in the large diameterhole and thereby decreasing differences in inner diameter hole sizebetween the small diameter hole and the large diameter hole.
 8. Themethod of claim 1, wherein the second process of isotropically etchingremoves the film by repeating a second sequence including: generating afirst plasma from a first gas which includes nitrogen, and isotropicallyforming a mixed layer of silicon and nitrogen that include an ionincluded in the first plasma in the inner surface of the holes;generating a second plasma from a second gas which includes fluorine andremoving the mixed layer by the second plasma.
 9. The method of claim 8,wherein the second gas is a mixed gas including NF₃ gas and O₂ gas. 10.The method of claim 8, wherein the second gas is a mixed gas includingNF₃ gas, O₂ gas, H₂ gas, and Ar gas or a mixed gas including CH₃F gas,O₂ gas, and Ar gas.
 11. The method of claim 8, wherein during thegenerating the first plasma with the first gas which includes nitrogen,the processing container is maintained at a pressure of 200 mTorr ormore, and a surface of the film is modified by nitrogen ions of thefirst plasma to form a modified surface, and the modified surfaceincludes the silicon nitride and is removed with the second plasma ofthe second gas which includes fluorine.
 12. The method of claim 11,wherein a process time of the generating the first plasma with the firstgas which includes nitrogen exceeds a self-control process time suchthat forming of the modified surface is uniformly performed regardlessof hole size.
 13. A method comprising: providing a workpiece includingan etching layer and a mask disposed on the etching layer, the maskhaving a first mask hole and a second mask hole, the first mask holehaving a first initial diameter, the second mask hole having a secondinitial diameter, the second initial diameter being larger than thefirst initial diameter, a difference between the first initial diameterand the second initial diameter defining an initial size difference;performing a first sequence on the mask, the first sequence including:performing a plasma OM on the workpiece to form a film on the first maskhole and the second mask hole, the first mask hole with the film havinga first post-CVD mask diameter, the second mask hole with the filmhaving a second post-CND mask diameter, the film having a firstthickness on the first mask hole and a second thickness on the secondmask hole, the first thickness being smaller than the second thickness;and isotropically etching the film to adjust the first post-CVD maskdiameter to form an adjusted first post-CVD mask diameter and to adjustthe second post-CND mask diameter to form an adjusted second post-CVDmask diameter, wherein a difference between the adjusted first post-CVDmask diameter and the adjusted second post-CVD mask diameter defining apost-etch size difference and the post-etch size difference is smallerthan the initial size difference.
 14. The method of claim 13, whereinthe workpiece includes a processing target layer below the mask, themethod further including etching the processing target layer through themask after performing the first sequence.
 15. A method of processing aworkpiece, the method comprising: a first sequence including: a firstprocess of forming a film on a sidewall of an inner surface of each of aplurality of holes formed in the workpiece; and a second process ofetching the film, wherein the first process of forming forms a firstfilm on the sidewall of the inner surface of the hole, and a second filmon the first film, and wherein each of the first and second films have athickness in a direction extending away from the sidewall, wherein anetching resistance of the first film is lower than an etching resistanceof the second film in the second process of isotropically etching,wherein during the second process, the second film is etched along thesidewall to reduce the thickness of the second film, wherein theplurality of holes include a first plurality of holes and a secondplurality of holes, and wherein the first and second processes areperformed on both the first plurality of holes and the second pluralityof holes, and during the second process of etching: the thickness of thesecond film in the first plurality of holes is etched through to exposethe first film prior to etching through the thickness of the second filmin the second plurality of holes; after exposing the first film in thefirst plurality of holes, continuing the second process of etching toetch the thickness of the first film in a direction toward the sidewallin the first plurality of holes while continuing etching of thethickness of the second film in the second plurality of holes, andwherein during the continuing the second process of etching an amount ofdecrease in thickness in the first film in the first plurality of holesis larger than an amount of decrease in thickness in the second film ofthe second plurality of holes and an increase in hole diameter of thefirst plurality of holes is larger than an increase in hole diameter ofthe second plurality of holes.
 16. The method of claim 15, wherein priorto the first process and the second process, the first plurality ofholes have inner diameters smaller than the second plurality of holes,and wherein after the first process and the second process differencesin inner hole diameters between the first plurality of holes and thesecond plurality of holes is decreased compared to prior to the firstprocess and the second process.
 17. The method of claim 15, wherein theworkpiece includes a processing target layer beneath the first pluralityof holes and the second plurality of holes, the method furtherincluding: processing the processing target layer through the firstplurality of holes and through the second plurality of holes afterperforming the first process and the second process.
 18. The method ofclaim 17, wherein the processing of the processing target layer includesetching the processing target layer through the first plurality of holesand the second plurality of holes.
 19. The method of claim 18, whereinthe first plurality of holes and the second plurality of holes areprovided in a mask positioned above the processing target layer.